What does IRBM stand for? 

irbm

An intermediate-range ballistic missile (IRBM) is a ballistic missile with a range of 3,000–5,500 km (1,864–3,418 miles), between a medium-range ballistic missile (MRBM) and an intercontinental ballistic missile (ICBM). Classifying ballistic missiles by range is done mostly for convenience; in principle there is very little difference between a low-performance ICBM and a high-performance IRBM, because decreasing payload mass can increase range over ICBM threshold. The range definition used here is used within the U.S. Missile Defense Agency. Some other sources include an additional category, the long-range ballistic missile (LRBM), to describe missiles with a range between IRBMs and true ICBMs. The more modern term theatre ballistic missile encompasses MRBMs and SRBMs, including any ballistic missile with a range under 3,500 km (2,175 mi). The progenitor for the IRBM was the A4b winged rocket, based on the V-2 (officially called A4) rocket used by Nazi Germany at the end of World War II.

see more »